Author: Vincent Diepeveen
Date: 10:42:05 07/25/05
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On July 25, 2005 at 09:22:48, Eberhard wrote: >If Blue Gene was a chess playing computer, how high could it score against Hydra >and the top 10 human chess players? Blue gene is constructed from 700Mhz processors which are pretty ugly for chess, and they have poor latencies to each other cpu in the 2048 processor rack they are consisted of. So it's in reality 2048 processors of 700Mhz. First of all the only program working at it would be Diep, not Hydra. Secondly no other modern program can run at it. Third a quad opteron dual core is of course going to outperform it, as you never get testing time on a blue gene system. It is very difficult to get a positive speedup out of 2048 processors. I doubt Diep would work well at it. To get Diep to work well at it, i would need another few months of hard programming, to modify something that already works good on 512 processors. A major problem of such hardware is that each processor is evaluating and searching positions much faster than a remote lookup of a single position to other processors costs. So you can't share any type of hashtable between them. Hydra has that problem too. At the 512 processor machien the only reason i could communicate easily with other processors is because diep was getting 20k nps a processor (it was 500Mhz cpu's). That is a slow speed. At more modern cpu's the speed is higher and with 2048 processors the total amount of requests from and to processors for hashtable information is too big to handle for such a machine. The latency to get just 1 position is just ugly. IBM can write fantastic stories on paper, but in reality it'll be more like 20 us (20 microseconds), just to get a single position from a remote processor. The routers are optimized for bandwidth and not for latency, all those things you fight against. So at such a system the effiency at which you search is more like 1% or so from the total node count. Hydra i estimate at 5% efficiency. So 100 nodes in hardware in reality are 5 nodes in software.
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